A transistor is an essential device that are used in all electronic circuits. There are various kinds of transistors, and the transistors are categorized by BJTs (Bipolar Junction Transistor) and FETs (Field Effect Transistor).
The BJT is a bipolar device and a current control device, and the FET is a unipolar device and a voltage control device. Among the FETs, a transistor that is frequently used in recent years is a MOSFET (Metal Oxide Semiconductor Field Effect Transistor).
FIG. 1 schematically illustrates an example of a configuration of a MOSFET transistor according to the related art. As illustrated in FIG. 1, a MOSFET 100 includes a gate 101, a source 102, and a drain 103 that are formed on a semiconductor substrate 105. When a voltage is applied to the gate 101, a channel 104 is formed between the drain 103 and the source 102 to allow electric charges to move. For example, when the substrate 105 is a P-type semiconductor and the source 102 and the drain 103 are doped as N-type semiconductors, a N-channel is formed.
FIG. 2 schematically illustrates an example of a configuration of a BJT transistor according to the related art. As illustrated in FIG. 2, a BJT 200 includes a base 201, an emitter 202, and a collector 203 that are formed on a substrate 205. In the BJT 200, currents flow due to differences in electron concentrations between the base 201, the emitter 202 and the collector 203. For example, when the emitter 202 and the collector 203 are doped as N-type semiconductors and the base 201 is doped as a P-type semiconductor, an N-type BJT is formed.
The two kinds of transistors have merits and demerits. The MOSFET has the merits in that power consumption is low and it is easy to integrate, whereas the BJT has the merit in that an operation speed is fast. In order to use all the merits of the MOSFET and the BJT, it may be considered that the two transistors are combined. However, since the MOSFET and the BJT are manufactured by different processes from each other, it is difficult to combine the two transistors. Accordingly, in general, one kind of transistor appropriate for a circuit to be used is selected and used.
A technology which is a background of the present invention is described in Korean Patent Publication No. 1998-086423 (Dec. 5, 1998) which is Patent Literature 1. Patent Literature 1 discloses a technology of a combination-type transistor in which the MOSFET and the BJT are combined. Patent Literature 1 discloses a combined MOS/bipolar transistor used in a BiCMOS circuit. However, the transistor of Patent Literature 1 has demerits in that a manufacturing process is complicated and it is high cost. Accordingly, there is a need for development of a combination-type transistor of the MOSFET and the BJT that can be simply manufactured with ease.